Mill and classifier



NOV. 30, 1937. J, c Es 2,100,734

MILL AND CLASSIFIER Filed Feb. 5, 1936 2 Sheets-Sheet l /1 1:; f I 1 I 1 Z9: Q Q I Imfenfiair ioe 61 255 Nov. 30, 1937. J. CRITES 2,100,734

' MILL AND 'CLASSIFIER' V Filed Feb. 5, 1936 2 Sheets-Sheet 2 Imkn'fi J59 (3217 Patented Nov. 30, 1937 UNI D STATES PATENT OFFICE AND CLASSIFIER Joe Crltes; Evanstourm" usignor, by meme assignments, to Combustion Engineer-[upcom- -may, Inc.,- a corporation of Delaware Application February 5, 1936. Serial, No;- 82,450

8 Claims.

This invention 'relate's'to certain new. and use In] improvements in a classifier, more particuor finely divided material from the mill in suspension in an air stream which is introduced into the upper portion of the classifier cone with a whirling motion. The heavier material is thrown outwardly against the walls of the classifier and then gravitates downwardlytoward an outlet opening in the lower end of the cone and is discharged through this opening back into the mill. The air stream, with the more finely divided material in suspension, passes out through a second discharge 20 opening in the upper central portion of the classi* fier.

' through the mill and classifier, there is a tend.-

ency for air to flow directly upwardly from the mill through the lower dischargeopening of the classifier and carry heavy material or tailings out through the discharge opening in the top of the classifier. To prevent this, some closure-means such as a fiap valve or gate, or a rotary feeder, has heretofore been used in the lower discharge opening of the classifier. According to the preslower portions of the conical walls to prevent solid material that is moving downwardly adjacent these walls from being carried upwardly by a central air stream, together-with a conical deflector positioned centrally within the classifier above the lower discharge opening so as to cause any air flowing upwardly through this bottom opening to move outwardly toward the side walls with a whirling motion and thereby be relieved of any suspended material.

The general object of this invention is to provide an improved classifier of the type briefly described hereinabove and disclosed more in detail in the specifications which follow;

Another object is to provide improved means for facilitating the discharge of tailings through the normally open lower discharge outlet of the classifier.

Another object is to provide improved means for properly classifying the material in a classifier of this cyclone type.

Another object is to provide improved means for permitting a cyclone classifier of this type to Since there is an upward draft or air-flow ent invention this discharge opening is normally left open, but spiral vanes are mounted on the classifier and a portionoi. the mill.

be used in direct open communication with a mill or pulverizer.

Other objects and advantages 01' this invention will be more apparent from the following detailed description of one approved form of mill and classifier combination constructed and operating according to the principles of this invention.

In the accompanying drawings:

.Fig. 1 is a central vertical section through the Fig. '2 is a horizontal section, on a somewhat larger scale, taken substantially on the line 2-2 I of Fig. 1. I

Fig. 3 is a partial side elevation and partial central vertical section, taken substantially on t e line 3-3 01 Fig. 1.

Fig. 4 is a partial top plan view and partial horizontal section taken substantially on the line H of Fig. 3.

Fig. 5 is a perspective view, partially broken away, showing the central conical deflector and its supporting stem. v

The apparatus assembly here shown comprises in general the mill A, the improved classifier B, and the'conduit C through which'the finely divided material suspended in an air stream is delivered from the classifier. It will be understood that a suitable blower or exhauster is connected somewhere in this circuit, usually in the conduit C, for drawing or forcing an air stream through the mill and classifier and thence through conduit C.

The mill or pulverizer A may be of any suitable type,-the one here shown by way of example being a bowl millsuch as is disclosed and claimed in the copending application of this inventor, Serial No. 25,789,1iled June 10, 1935. Briefly described, this mill comprises a substantially closed casing l in which the bowl 2 is carried by vertical shaft 3 for rotation about the central vertical axis a of the mill and classifier. The annular side wall I of the bowl 2 slopes upwardly at a. very steep angle and carries the internal grinding ring 5 against which the material is ground by a plurality of grinding rollers 6. In the present example there are two of these rollers 6 each supported for free rotation on the lower portion of a shaft 1 the upper end of which is fixed in a supporting lever 8 mounted on shaft 9 pivoted in bearing brackets i0 mounted on plate H removably. secured over an opening 52 in the top it of the mill housing. The mechanism indicated generally at It and confined between the outer end of lever 8 and the fixed bracket i5, comprises a spring l6 adapted to urge the roller toward 55 the grinding ring 5, and an adjustable limiting rod il adapted to limit the movement of the roller toward the ring so as to provide a small clearance and prevent pounding of the metallic surfaces when there is no material to be ground cated generally at D (Fig. 3) and comprising the hopper I8, the rotary feed wheel E9, the screw I conveyor 20, and the chute 2! which delivers the material into the center of bowl 2.

It will be understood that the bowl 2 is rotated by any suitable means (not here shown) and that an air stream is admitted into the lower portion of housing I. The material to be ground is thrown outwardly against the side walls of the rotating bowl 2 and is caught between the grinding ring 5 and rollers B and ground or pulverized to a finely divided condition before it is thrown from the rotating elements and caught by the air stream passing upwardly through the mill. Material that is sufliciently pulverized to be carried in suspension is delivered into the classifier B as hereinafter described.

The inner shell of this improved classifier comprises the main conical portion 22 which converges downwardly to the lower central discharge outlet 23, and an upper cylindrical portion 24 which connects with the top wall 25. The relatively small bottom discharge outlet 23 is in open communication with the central portion of the mill housing so as to discharge tailings or insufiiciently pulverized material back into the central portion of the bowl 2. The upper outlet conduit C has an extension 28 which projects downwardly through the central portion of top wall 25 with its open lower end substantially at the level of the lower edge of cylindrical wall 23. An annular supply housing 21 surrounds the cylindrical wall 24 and communicates with the interior of the classifier housing through a circumferential series of ports 23 formed in wall 23.

Any suitable conduit means may be provided for delivering theair stream carrying the suspended material from the mill housing into the supply housing 21. In the present example two similar vertical conduits 29 extend from openings 30 in the top wall l3 of the mill and have upper flaring or fanned portions 29! which connect with the lower portion of housing 21. The feeder chute 2| extends down through one of these openings 30 in the top wall of the mill, in the example here shown.

As an alternative construction, the material laden air from the mill might be delivered upwardly through an outer cone surrounding the inner cone 22 and communicating at its lower end with the interior of the mill housing as is common in this art.

A series of vanes or baflles 3| are adapted to direct the air streams flowing inwardly through ports 28 so as to cause a whirling movement of the air within the classifier housing. Each of these baffles 3| is secured on a vertical shaft 32 at one side of one of the ports 28, this shaft 32 extending upwardly through top wall 25 and carrying an arm 33 adjustable at 34 along an arcuate clamping means 35 so as to determine the angle at which the vane or bafile 3| projects into the classifier housing. These baflles should all be inclined' in the same direction and are preferably arranged substantially tangential to the outlet tube 26, as best shown in Fig. 4.

The operation of the classifier as thus far described does not differ materially from other classifiers of this cyclone type. The materialladen air flowing upwardly from the millhousing through conduits 29 and supply housing 21 enters the classifying housing through ports 28, and a whirling motion within the classifying housing is imparted to'this air by the deflecting baiiies 3!. The air will whirl in a clockwise direction as seen from above. This whirling motion tends, by centrifugal force, to throw out the heavier material particles or tailings", and these heavier particles gravitate down the side walls 22 and thence through chute 23 back into the mill housing. The air-stream (still carrying in suspension the finer pulverized material) finds its I way downwardly and then upwardly toward the central portion of the casing and out through tubular member 26 and conduit 0.

Since there is an upward suction of air through classifier B from the mill housing, there will be a tendency for air to be drawn upwardly through the open discharge passage 23 and thence up through the center of the classifier housing and directly out through conduit C. This central air stream will tend to pick up some of the heavier material that should be discharged downwardly through spout 23 and carry this material out through conduit C. In order to prevent this, it has been customary hitherto to provide a suitable flap gate or valve, or a rotary feeder, in the spout 23 so asto normally prevent the upward fiow of air through this passage while permitting solid material to be dumped downwardly at suitable intervals. These flap gates are rather uncertain in their operation and require some substantial head of material above the gateto make them work satisfactorily. Also, with varying air pressures in the system these gates require adjustment. A

rotary feeder requires an extra drive and also there is considerable wear due to the rotary member dragging through the coarse tailings that are being returned to the mill. Also, large pieces of foreign material are apt to jam these valves or gates thus allowing air to flow up through the passage and carry coarse material upwardly out of the classifier.

The object of the present invention is to do away with such valve means and leave the supply chute or passage 23 normally open, while at the same time providing means for preventing heavier material from being carried upwardly through the classifier. To accomplish this, a plurality of spiral vanes 36 are mounted Within the lower portion of the invertedconical member 22. In the present example there are two of these vanes, each being about three-quarters of a turn (that is 270) in length. These vanes pitch downwardly in the direction of rotation of the whirling gases (that is in the direction of a right-hand threaded screw as viewed from above). These vanes are attached to and carried by the inner side walls of the cone and preferably slope downwardly in a transverse or radial direction at substantially an angle of 30 to the horizontal. As a result, any material thrown outwardly against the side walls of the cone will be pocketed beneath these vanes. It will be noted that since the air within the classifier is whirling in a clockwise directidn, the solid material thrown outwardly against the side walls also tends to spiral downwardly along these walls, and when this material reaches the lower portion of the cone it will be caught beneath the vanes 36 and thereoutlet opening 23.

supported centrallywithin the classifier chamber is a hollow conicaldefiector I! with its larger end at the bottom and substantially at. the level of the upper ends of vanes 38. This cone is supported by a stem I! attached to the closed smaller upper end of the conewthe stem projecting upwardly in line with the central axis a and bein supported by a spider II secured within the outletconduit extension 28. This conical defiecto'r' serves a two-fold functionr In the first place,

its tapered upper surface tends to puncture the cone 22, and the coarse materials that have been picked up by this upwardly flowing air current will be thrown outwardly against the walls of cone 22 and caughtbeneath the vanes 36 and thus carried downwardly again toward the discharge outlet. As a result substantially none of the heavier material or tailings can be carried upwardly through the central portion of the classifier'even though the bottom discharge outlet 23 is open at all times. However, such of the fine materials as might otherwise be carried down by the coarser material through the discharge opening is carried upwardly by the central air stream and out through conduit C. In this way practically all of the sumciently pulverized material is taken out by the classifier, and all .0! the coarse material is'returned to the mill. It will be noted that this classifier has no movlnagpartsv and when once properly adjusted needs pracwhich the air stream-carries the lighter solid material in suspension, and a lower normally open discharge opening through which heavier solid I material gravitates back into the mill and through which a central air stream is drawn upwardly from the mill, spiral vanes positioned along the lower inner walls of the classifier adjacent the open loweroutlet and a cooperating deflector positioned centrally above the lower opening for preventing the upward carrying oi heavier material through the upper outlet in suspension in the air stream flowing upwardly from the mill 'for upwardly flowing gases and fine material carried thereby in suspension, said outlet passage leading centrally from the top wall, means for projecting material-laden gases' into the upper portion or the shell in suchdirectionas to cause a whirling motion about the central vertical axis of the classifier, spiral vanes mounted on the ina mill comprising a.

nei surface of the lower conical wall, said vanes being pitched downwardly with respect to the direction of rotation of the whirling gases and also slanting downwardly from the conical wall toward the central axis, and a cooperating defiector positioned centrally above the lower discharge passage for forcing gases flowing upwardly through this lower opening toward the conical side wall 3. In a classifier, a shell comprising a top wall and side walls the lower portions of which'converge downwardlyin. the form of an inverted cone, an open discharge passage leading from the smaller lower ,end of the cone, an outlet passage for upwardly flowing gases and fine material carried thereby in suspension, said outlet passage leading centrally from the top wall, means for projecting material-laden gases into the upper portion of theshell in such direction as to cause a whirling motion about the central vertical axis of the classifier, spiral vanes mounted on the inner surface of the lower conical well, said vanes being pitched downwardly with respect to the direction of rotation of the whirling gases, and a hollow conical deflector supported centrally within the conical shell with its lower larger open end above the lower discharge passage.

4. In a classifier, a. shell comprising a top wall and side walls-the lower portions of which converge downwardly in the form of an inverted cone, an open discharge passage leading from the smaller lower end or the cone, an outlet passage for upwardly flowing gases and fine material carried in suspension thereby, said passage-leading centrally from-the top wall, a supply housing surrounding the upper portion of the shell and having a circumferential series of inlet ports communicating with theinterior of the shell, means for conducting material-laden gases into the supply housing, deflecting means positioned adjacent the inlet ports tor imparting a whirling motion about the central vertical axis of the classifier to the gases and materials introduced through the ports, spiral vanes mounted on the.

inner surface of the lower conical wall, said vanes being pitched downwardly with respect to the direction of rotation of. the whirling gases and also slanting downwardly from the conical wall toward the central axis, and a cooperating de-,

fiector positioned centrally above the lower dischange passage for forcing gases flowing upwardv1y through this lower opening toward the conical side wall. a f

5. In a classifier, a shell comprising atop wall and sidewalls the lower portions of which converge downwardly in the form of an inverted cone, an open discharge passage leading from the smaller lower end of the cone, an outlet passage for upwardly flowing gases and fine material carried in suspension thereby, said passage leading centrally from the top wall, a supply housing surrounding the upper portion of the shell and having a circumferential series of inlet ports communicating with the interior of the shell, means for conducting material-laden gases into the supply housing, deflecting means positioned adjacent the inlet ports for imparting a whirling motion about the central vertical axis of the classifier to the gases and materials introduced through the ports, spiral vanes mounted on the inner surface of the lower conical wall, said vanes being pitcheddownwardly with respect to the direction of rotation of the whirling gases, and a hollow conical deflector supported centrally within the conical shell with its lower larger open end above the lower discharge passage.

6. In combination with a mill comprising a closed housing and means therein for pulverizing material, a classifier comprising a shell having a top wall and side walls the lower portions of which converge downwardly in the form of an inverted cone, an open discharge passage leading from the lower end of the cone into the central portion of the mill housing, an outlet passage for upwardly fiowing gases and fine material carried in suspension thereby, said passage leading centrally from the top wall of the classifier, a

supply housing surrounding the upper portion of the shell and having a circumferential series of inlet ports communicating with the interior of the shell, open conduit means for material-laden gases leading from the interior of the mill housing to the'supply housing, deflecting means positioned adjacent the inlet ports for imparting a whirling motion about the central vertical axis of the classifier to the gases and materials introduced through the ports, spiral vanes mounted on the inner surface of the lower conical wall,

said vanes being pitched downwardly with respect to the direction of rotation of the whirling gases and also slanting downwardly from the conical wall toward the central axis, and a coopcrating deflector positioned centrally above thelower discharge passage for forcing gases flowing upwardly through this lower opening toward the conical side wall.

'7. In combination with a mill comprising a closed housing andmeans therein for'pulverizing .material, a classifier comprising a shell having a top wall and side wall the lower portions of which converge downwardly in the form of an inverted cone, an open discharge passage leading from the lower end of the cone into the central portion of the mill housing, an outlet passage for upwardly flowing gases and fine material carried in sus pension thereby, said passage leading centrally from the top wall of the classifier, a supply hous ing surrounding the upper portion of the shell and having a circumferential series of inlet ports communicating with the interior of the shell, open conduit means for material-laden gases leading from the interior of the mill housing to the supply housing, deflecting means positioned adjacent the inlet ports for imparting a whirling,

motion about the central vertical axis of the classifier to the gases and materials introduced through the ports, spiral vanes mounted on the inner surface of the lower conical wall, said vanes being pitched downwardly with respect to'the direction of rotation of the whirling gases, and a hollow conical deflector supported centrally within the conical shell with its lower larger open end above the lower discharge passage.

8. In a classifier comprising a casing, means 7 for projecting material laden gases into the upfor preventing the upward carrying of heavier material in suspension in the gas stream that is sucked upwardly throughthe central portion of the lower outlet opening.

JOE CRITES. 

